The structural role of gamma-carboxyglutamic acid in the vitamin K-dependent blood coagulation proteins is being evaluated by an immunologic approach employing conformationally-specific antibodies and by natural abundance 13C nuclear magnetic resonance spectroscopy. These studies are performed on gamma-carboxyglutamic acid, synthetic peptides containing gamma-carboxyglutamic acid, proteolytic fragments of factor X and prothrombin, and native factor X and prothrombin.